Study of Intravenously (IV) Infused Etentamig in Combination With an Oral Cereblon E3 Ligase Modulatory Drug (CELMoD) Agent Assessing Adverse Events and Change in Disease Activity in Adult Participants With Relapsed or Refractory Multiple Myeloma

Phase 1: Dose-Limiting Toxicities (DLT)s of Etentamig when given in Combination with Iberdomide in Participants with Relapsed/Refractory Multiple Myeloma (RRMM)

Timeframe: Up to Approximately 56 Days

DLT events are defined as clinically significant adverse events or abnormal laboratory values assessed as unrelated to disease progression, underlying disease, intercurrent illness, or concomitant medications.

Number of Participants with Adverse Events (AE)s

Timeframe: Up to Approximately 129 Months

An adverse event is defined as any untoward medical occurrence in a participant or clinical investigation participant administered a pharmaceutical product and which does not necessarily have a causal relationship with this treatment.

Partial Response (PR) Response Rate (RR)

Timeframe: Up to 3 Years

PR is defined \>= 50% reduction of serum M-protein and reduction in 24-hour urinary M-protein by \>= 90% or to \< 200 mg per 24 hours, if the serum and urine M-protein are unmeasurable, a \>= 50% decrease in the difference between involved and uninvolved FLC levels is required in place of the M-protein criteria, if the serum and urine M-protein are unmeasurable, and serum free light assay is also unmeasurable, a \>= 50% reduction in plasma cells is required in place of M-protein, provided baseline bone marrow plasma cell percentage was \>= 30%, \>= 50% reduction in the size of soft tissue plasmacytomas is also required, if present at baseline.

Very Good Partial Response (VGPR) RR

Timeframe: Up to 3 Years

VGPR is defined as serum and urine M-protein detectable by immunofixation but not on electrophoresis or \>= 90% reduction in serum M-protein plus urine M-protein \< 100 mg per 24 hours, for participants in whom the only measurable disease is by serum free light chains (FLC) levels, VGPR is defined as \>= 90% decrease in the difference between involved and uninvolved FLC levels.

Complete Response (CR) RR

Timeframe: Up to 3 Years

CR is defined negative immunofixation on the serum and urine (regardless of whether disease at baseline was measurable on serum, urine, both, or neither), disappearance of any soft tissue plasmacytomas, \< 5% plasma cells in bone marrow, and for participants in whom the only measurable disease is by serum FLC levels, a normal FLC ratio is also required.

Stringent Complete Response (sCR) RR

Timeframe: Up to 3 Years

sCR is defined negative immunofixation on the serum and urine (regardless of whether disease at baseline was measurable on serum, urine, both, or neither), disappearance of any soft tissue plasmacytomas, \< 5% plasma cells in bone marrow, normal FLC ratio and absence of clonal cells in bone marrow by immunohistochemistry (kappa/lambda ratio \<= 4:1 or \>= 1:2 for kappa and lambda participants, respectively, after counting \>= 100 plasma cells).

Overall Response Rate (ORR)

Timeframe: Up to 3 Years

ORR (PR + VGPR + CR + sCR) will be defined as the proportion of participants who achieved a PR or better.

Progression-Free Survival (PFS)

Timeframe: Up to 3 Years

PFS is defined as the number of days from the date of first dose to the date of earliest disease progression or death.

Duration of Response (DOR)

Timeframe: Up to 3 Years

DOR is defined as the number of days from the date of first response (sCR, CR, VGPR, or PR) to the earliest recurrence, progressive disease, or death, whatever occurs first.

Time-to-Progression (TTP)

Timeframe: Up to 3 Years

TTP will be defined as the number of days from the date of first dose to the date of earliest disease progression.

Minimal Residual Disease (MRD) negativity

Timeframe: Up to 3 Years

The MRD negativity rate is defined as the proportion of participants who achieve MRD negative status.